Often1

1. Once a carrier proposes it's carryon policy, it is adopted by FAA and a violation (by the carrier) can result in fines to the carrier (as well as individual GA and FA). That needs to happen on a random and routine basis. Only way to make this work is to make it genuinely and individually costly.

2. Not only is the OH issue a problem in terms of fairness, but it has turned the boarding process into a nightmare. Back in the old days, F boarded last, not first under the theory that nobody wants to sit in their seat on the ground. But for OH space, I would just as soon be the last pax to board.

3. Solution lies in enforcing the sizer rules. Over-sized bags get gate-checked (no matter how empty the flight). And, gate-checked bags go to baggage office, not carousel, at final destination. The bag fee + a penalty (no freebies for status, cc holders and the like) is assessed at the baggage office so that the GA's don't stand around delaying the flight. Let those who break the rules wait for 90 mins. at destination to pay triple the bag fee.

4. Needless to say, there are occasions where a bag fits the sizer but can't be acommodated due to aircraft size or the simple fact that there are too many roll-a-boards even of the right size. Those bags ought to be gate-checked just like wheelchairs and strollers. They are brought to the jet bridge.

It is possibly true that there are occasional first-time flyers who can't figure out the rules, but it's clear that most of those lugging steamer trunks into the OH are experienced travelers who know excactly what they are doing and know that it's wrong. There's a way to deter the conduct.